Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://digital.libraries.psu.edu/iiif/info/maps1/10396/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-130f4969-aa2f-42ea-a9fd-b81439401614",
      "cw-c82a26f1-ae5d-403c-9b81-ea8285a80505"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e7390244-9b6a-4646-bf50-7c88c50a8c25",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/10396/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-c82a26f1-ae5d-403c-9b81-ea8285a80505"
  }
}